package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.util.PriorityQueue;

/**
 * A {@link HitCollector} implementation that collects the top-scoring
 * documents, returning them as a {@link TopDocs}. This is used by {@link
 * IndexSearcher} to implement {@link TopDocs}-based search.
 * 
 * <p>
 * This may be extended, overriding the collect method to, e.g., conditionally
 * invoke <code>super()</code> in order to filter which documents are
 * collected.
 */
public class TopDocCollector extends HitCollector {

	private ScoreDoc reusableSD;

	int totalHits;
	PriorityQueue hq;

	/**
	 * Construct to collect a given number of hits.
	 * 
	 * @param numHits
	 *            the maximum number of hits to collect
	 */
	public TopDocCollector(int numHits) {
		this(numHits, new HitQueue(numHits));
	}

	TopDocCollector(int numHits, PriorityQueue hq) {
		this.hq = hq;
	}

	// javadoc inherited
	public void collect(int doc, float score) {
		if (score > 0.0f) {
			totalHits++;
			if (reusableSD == null) {
				reusableSD = new ScoreDoc(doc, score);
			} else if (score >= reusableSD.score) {
				// reusableSD holds the last "rejected" entry, so, if
				// this new score is not better than that, there's no
				// need to try inserting it
				reusableSD.doc = doc;
				reusableSD.score = score;
			} else {
				return;
			}
			reusableSD = (ScoreDoc) hq.insertWithOverflow(reusableSD);
		}
	}

	/** The total number of documents that matched this query. */
	public int getTotalHits() {
		return totalHits;
	}

	/** The top-scoring hits. */
	public TopDocs topDocs() {
		ScoreDoc[] scoreDocs = new ScoreDoc[hq.size()];
		for (int i = hq.size() - 1; i >= 0; i--)
			// put docs in array
			scoreDocs[i] = (ScoreDoc) hq.pop();

		float maxScore = (totalHits == 0) ? Float.NEGATIVE_INFINITY
				: scoreDocs[0].score;

		return new TopDocs(totalHits, scoreDocs, maxScore);
	}
}
